Reflectors are used in various products in order to use light more effectively. Recently, many products include a light source in the form of a semiconductor, i.e. semiconductor laser, light emitting diode (hereinafter, LED), and the like, to allow miniaturization of the device and light source. Reflectors for LEDs and resin compositions for the preparation thereof can require properties such as high light reflectance, high whiteness, good moldability, high dimensional stability, high mechanical strength, high heat resistance and the like.
For example, reflectors used for LEDs can require not only mechanical strength but also heat resistance because the reflectors are surface mounted onto, for example, a printed circuit board. Reflectors for LEDs can also require excellent moldability due to the miniaturization of the device. Also, reflectors can require high surface reflectance, and in particular the ability to inhibit the degradation of surface reflectance due to exposure to heat during the process of assembling the LED and the process of reflow soldering. Also, reflectors can be made using a particular insert molding method to obtain a reflector with high surface reflectance, and accordingly a resin composition which can be used in such a method can also be required.
Conventionally, liquid crystal polymers (LCPs) or heat-resistant polyamide resins were used as materials able to resist temperatures during reflow soldering using lead-free solder (typically 260° C.). LCP has excellent in heat resistance, light stability and moldability. However, adhesion of the LCP with a sealing resin such as epoxy resin, which is used after mounting the LED to the reflector, can deteriorate. Also, LCPs can have low whiteness and thus it can be difficult to provide high surface reflectance thereto.
Aliphatic polyamides (such as PA6, PA66, PA11, and PA12) can have excellent mechanical strength properties and injection moldability. Aliphatic polyamide resins, however, do not have heat resistance sufficient to resist temperatures during reflow soldering and further cannot have low hygroscopicity. Also aliphatic polyamides can suffer deteriorated surface reflectance due to discoloration that can occur during heating.
International Patent Application Publication No. 2003-085029 and Japanese Patent Application Publication No. 1995-228776 are directed to a resin composition for reflectors comprising polyamide resin consisting of 1,9-diaminononane and inorganic filler. However, the resin composition does not adhere well to a sealing resin.
Japanese Patent Application Publication No. 2002-294070 is directed to a polyamide resin including potassium titanate fiber and/or wollastonite. However, the resin does not have sufficient strength when molding, and it can be difficult to use when insert molding.
Japanese Patent Application Publication No. 2004-075994 is directed to a polyamide composition useful for articles and lamp reflector materials with high whiteness and high surface reflectance. The polyamide composition has higher heat resistance than a resin composition using a conventional heat-resistant polyamide such as PA6T or PA46 and the like, but it does not completely solve the discoloration problem resulting from exposure to heat.